Stoving lacquers

ABSTRACT

THE PRESENT INVENTION RELATES TO STOVING LACQUERS FOR THE COIL COATING PROCEDURE COMPRISING ORGANIC SOLVENTS AND FILM-FORMING COPOLYMERS OF STYRENE, ACRYLIC ACID OR METHACRYLIC ACID, N-ALKOXYALKYLACRYLIC ACID AMIDES OR N-ALKOXYALKYLMETHACRYLIC ACID AMIDES, HYDROXYALKYLACRYLATE OR HYDROXYALKYL METHACRYLATES, ETHYLACRYLATE AND METHYLME;THACRYLATE, THE COPOLYMERS OF WHICH ARE STILL SOLUBLE IN ORGANIC SOLVENTS AND HAVE BEEN PRODUCED IN A TWO-STEP METHOD. THESE STOVING LACQUERS ARE USED FOR LACQUERING ROLLED TINPLATE FOR STRIPS OF TIN-PLATE WHICH CAN BE COILED UP AND SHAPED AND PUNCHED BY THE PROCESSOR, WITH THE LACQUERING REMAINING UNDAMAGED EVEN ON STRETCHED AND PUNCHED SURFACE (COIL COATING PROCESS).

United States Patent Office 3,812,067 Patented May 21, 1974 US. Cl. 260-285 R 15 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to stoving lacquers for the coil coating procedure comprising organic solvents and film-forming copolymers of styrene, acrylic acid or methacrylic acid, N-alkoxyalkylacrylic acid amides or N-alkoxyalkylmethacrylic acid amides, hydroxyalkylacrylate or hydroxyalkyl methacrylates, ethylacrylate and methyl- 'methacrylate, the copolymers of which are still soluble in organic solvents and have been produced in a two-step method. These stoving lacquers are used for lacquering rolled tinplate for strips of tin-plate which can be coiled up and shaped and punched by the processor, with the lacquering remaining undamaged even on stretched and punched surfaces (coil coating process).

CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part application of application Ser. No. 229,183, filed Feb. 24, 1972 in the US. Patent Oflice, now abandoned. Applicants claim priority of applications Ser. Nos. 2,866/71 and 1,057/72, filed Feb. 26, 1971 and I an. 25, 1971, respectively, in the Swiss Patent Oflice.

BACKGROUND OF THE INVENTION (1) Field of the invention The stoving lacquers of this invention are especially distinguished in that they have an improved pigment binding capacity and that the lacquerings manufactured with them develop their valuable properties practically completely already at relatively short stoving times (for examples 1 to 3 minutes) at 260 C. Furthermore, lacquers manufactured from each copolymers yield lacquerings of improved adhesion and impact strength having particularly pronounced elasticity and hardness. Lacquerings are obtained which also possess other properties, such as light resistance, flexural strength, and solvent resistance to an exceptional degree. Since the valuable properties of the lacquerings manifest themselves especially on metals such as iron, aluminum, magnesium and alloys of these metals, the stoving lacquers are above all suitable for lacquering articles made of sheet metal, for example parts of coach- Work, boats and refrigerators and also cans, jugs, buckets and for industrial and domestic appliances. The stoving lacquers can be used equally well for the production of primer coats and of top coats. Because of their adhesion, they are furthermore very suitable for the manufacture of one-coat lacquerings on metal, and the high surface gloss in general makes subsequent polishing superfluous.

(2) Prior art German Published Specification 1,102,410 discloses stoving lacquers which contain (I) Organic solvents and (H) Copolymers of (A) esters of acrylic or methacrylic acid with alkanols,

(B) ethers of N-methylolacrylic acid amide or N-methylolmethacrylic acid amide with alkanols or phenylalcohols,

(C) monoesters of acrylic or methacrylic acid with polyhyldric hydroxy compounds and optionally additionally (D) other compounds possessing an ethylenically unsaturated copolymerizable group, such as acrylonitrile, acrylic and methacrylic acid, higher esters of ethylenecarboxylic acids, styrene and vinyl acetate.

such stoving lacquers are distinguished by a series of valuable properties, however, they do not approach the lacquers of the present invention, as has been shown by Comparison Test 3. The cured coatings of the present invention show superior pendulum hardness and combined cross-cut and deep drawing values. Also no yellowing of the coatings can be observed.

US. Pat. 3,453,345 to Mabrey et al. claim a heat hardenable linear addition copolymer comprising an interpolymerization reaction product of a number of copolymerable monomers well-known. The Mabrey et al. patent discloses monomers, which are employed also by the present invention. There is, however, a very serious difference concerning the method of cross-linking the copolymer with the aid of the alkylol acrylamide residues in the linear polymer chains. Mabrey et al. form the alkylol acrylamide component in situ while copolymerizing all monomers. By this method a reproducible building in of the alkylol acrylamide and parallel thereto a reproducible structure of the polymerchain cannot be secured. Since the properties of a copolymer always depend mainly upon the sequence of the polymer chain, this becomes a very important factor. It has been discovered that improved stovable coating compositions are obtained when the polymerization mixture of the indicated monomesr contains the component (a), the ether of the N- methylolmethacrylamide with the C to C -alkanol present, per se in the mixture, in combination with the other ingredients.

That is, it has been discovered that, surprisingly superior physical properties in the coatings are obtained if the component (a) is prepared ahead of time, prior to reaction with the other monomers.

The advantages of this discovery are supported by Comparison Test 2 to of the present specication. In Test 2 the preparation and comparison of the stovable polymer coating composition is described in accordance with Example 4, compared to the composition of Example 3 of the Mabrey et al. patent. In the present invention shown in Comparison Tests. The Table shows that the coatings prepared according to Rohm and Haas and Mabrey do not have a completely cured and non-tacky surface. Yellowing of the Rohm and Haas and Mabrey coatings has also been observed. The most surprising difierence between the coatings of applicants and those of the Rohmand Haas and Mabrey manifests itself in a comparison of the pendulum hardness and the combined cross-cut and deep drawing values. Applicants lacquer compositions give excellent pendulum hardness and other desirable properties when applied as a coating and baked for only 3 minutes. The prior art lacquer compositions did not give nearly as good coating properties, even when baked for 30 minutes as required by Mabrey, a period which is not practical on an in-.

dustrial scale, and even under the longer baking time the prior art lacquer compositions were tacky and yellow.

3 SUMMARY Stoving lacquers for the coil coatings procedure com prising organic solvents and film-forming copolymers of styrene, acrylic acid or methacrylic acid, N-alkoxyalkylacrylic acid amides or N-alkoxyalkylmethacrylic acid amides, hydroxyalkylacrylate or hydroxyalkyl methacrylates, ethylacrylate and methylmethacrylate, the copolymers of which are still soluble in organic solvents and have been produced in a two-step method wherein (1) an ether of N-methylolacrylamide or N-methylolmethacrylamide is made by warming 1 mol of acrylamide of methacrylamide, 1 to 1.5 mols of paraformaldehyde, 1 to 3 mols of a saturated alcohol of 1 to 8 carbon atoms and maleic anhydride as the catalyst, and

(2) a mixture of (a) 4 to 11% by weight of this ether of N-methylolacrylamide or N-methylolmethacrylamide,

(b) 10 to 30% by weight of styrene,

(c) 1 to 3% by weight of acrylic acid or methylacrylic acid,

(d) 55 to 65% by weight of ethylacrylate,

(e) 5 to 20% by weight of methylmethacrylate and (f) 2 to by weight of hydroxyalkyl esters. of methacrylic acid or acrylic acid, of the following wherein n represents numbers between 2 and 6,

R is hydrogen or a methyl group and the compound of the formula (I) or its mixtures possess hydroxyl numbers of about 100 to about 200, and the sum of the percentages of components (a) to (f) is in each case 100, was poured over a period of about one to four hours into a solvent mixture heated to 80-l25 C. and consisting of a mixture of aromatic solventsof boiling point 180 C. to 270 C. and butyldiglycol or ethyldiglycol, the ratio of aromatics to glycol-ethers being between 1:1 and 2:1 parts by weight, under an inert gas, and the polymerization was then continued for approximately 2 to 8 hours in order to achieve as complete a conversion of the monomers as possible. A specially preferred embodiment of the invention concerns stoving lacquers wherein in step (2) the following mixture has been employed:

(a) 6 to 9% by weight of an ether of N-methylolacrylamide or N-methylolmethacrylamide with nbutanol,

(b) 10 to 20% by weight of styrene,

(c) 1 to 3% by weight of acrylic acid or methylacrylic acid,

((1) 55 to 65% by weight of ethyl acrylate,

(e) 5 to 20% by weight of methyl methacrylate and (f) 4 to 8% by weight of hydroxyalkyl esters of methacrylic acid, of the formula (I) already mentioned.

The most preferred embodiment is presented-by a stoving lacquer wherein in step (2) the following mixture has been employed:

(a) 5.8% by weight of the ether of N-methylolmethacrylamide with n-butanol,

(b) 10.2% by weight of styrene,

(c) 2.8% by weight of acrylic acid,

(d) 61.9% by weight of ethylacrylate,

(e) 17.1% by weight of methyl methacrylate and (f) 2.2% by weight of hydroxyalkylester of methacrylic acid of the formula (I) wherein n is 4.

For the most preferred embodiment the above mentioned' mixture of (a), (c),(d), (e), and (f) has to be poured continuously into a solvent mixture consisting of by weight of a mixture A of about 80% by weight of aromatic hydrocarbons and about 20% by weight of aliphatic hydrocarbons having a boiling point of between 208 and 254 C. and B of 40% by Weight of diethyleneglycolmonobutylether. The preferred admission temperature is between 90 and 100 C. The admission time of 2:0.5 hours of the monomer mixture into the solvent mixture, which is heated to 90 to 100 C. is preferred.

Tert.-butylperoctoate is the especially preferred polymerization initiator. The copolymerization is being controlled in the most preferred embodiment of the stoving lacquer by regulating the admission speed of the monomer mixture, the reaction temperature and the admission of the polymerization initiator, so that the obtained copolymer has a viscosity of about Z according to Gardner- Holdt, measured in a 51% strength by weight solvent mixture (consisting of A and B) at 20 C.

The most preferred embodiment of the stoving lacquers is being described by Example 2.

A special further embodiment of the stoving lacquers is characterized in that the copolymer contains a copolymerized ether of N-methylolmethacrylamide with isobutanol or, preferably n-butanol, which contains, in its solution, the catalyst or its esterification products, maleic anhydride having been employed as the catalyst.

As component (a), ethers of N-methylolacrylamide or N-methylolmethacrylamide with saturated alcohols having 1 to 8 carbon atoms, such as methanol, ethanol, propanol, n-butanol, isobutanol, pentanol, hexanol, heptanol, octanol or 2-ethylhexanol are contained.

Ethers of N-methylolacrylamide or N-methylolmethacrylamide with n-butanol are preferentially incorporated in the copolymer.

The particularly preferentially incorporated ether ofN- methylolmethacrylamide with n-butanol or isobutanol is obtained by a particularly suitable reaction of the reactants in the ratio of 1 mol of methaccrylamide, 1 to 1.5 mols of paraformaldehyde, 1 to 3 mols of n-butanol and maleic anhydride with warming and while largely removing water. A reaction product wherein the ratios of the reactants are 1 mol of methacrylamide, 1.2 mols of paraformaldehyde and 2 mols of n-butanol and 0.01 to 0.03 mol of maleic anhydride is the most suitable for incorporation into the copolymer. The reaction mixture of methacrylamide, paraformaldehyde, n-butanol and maleic anhydride which is employed yields, after reaction, approx. by weight :3% by weight of the ether of N-methylolmethacrylamide with -n-butanol and approx. 35% by weight i3% by weight of n-butanol, while in the reaction of methacrylamide, paraformaldehyde, isobutavnol and maleic anhydride a product of approx. 64% by weight i3% by weight of the ether of N-methylolmethacrylamide with isobutanol and approx. 36% by weight 23% by weight of isobutanol is obtained.

The most preferred embodiment of the stoving lacquers consists of employing, as the ether of N-methylolmethacrylamide with n-butanol, the reaction mixture solution obtained by reaction of 4 mols of methacrylamide, 4.67 mols of paraformaldehyde, 8 mols of n-butanol and 0.03 mol of maleic anhydride while removing water. Such a reaction batch contains approximately:

64.0% by weight of the ether of N-methylolmethacrylamide with n-butanol,

32.5% by weight of butanol,

0.8% by weight of paraformaldehyde,

1.6% by weight of water,

0.6% by weight of methacrylamide and 0.5% by weight of maleic acid monobutyl ester.

A further copolymer which also leads to a usable embodiment of the stoving lacquers is obtained if, as the ether of N-methylolmethacrylamide with isobutanol, the

reaction mixture solution obtained by reacting 4 mols of methacrylamide, 4.67 mols of paraformaldehyde, 8.0

mols of isobutanol and 0.03 mol of maleic anhydride,

while removing water, is employed for the copolymerization. 1

Such a reaction mix contains approximately:

63.4% by weight ofthe ether of N-methylolmethacryl amide with isobutanol,

33.0% by weight of isobutanol,

0.8% by weight of paraformaldehyde,

1.5% by weight of water, i

0.8% by weight of methacrylamide and 0.5% by weight of maleic acid monoisobutyl ester.

If the ether of N-methylolmethacrylamide with isobutanol is employed with the. monomeric compounds mentioned under (b) to (f), products are obtained which after stoving give hard surface lacquering. If, however, a product is desired which is to show more elastic properties after the stoving process, a copolymer with the ether of N-methylolmethacrylamide with n-butanol and the monomeric compounds mentioned under (b) to (f) is manufactured.

Ethyl acrylate is employed as the component (d).

.Methyl methacrylate is employed as the component (e).

Hydroxyalkyl esters of methacrylic acid ,or acrylic acid, the esterification products of methacrylic f acid or acrylic acid and polypropylene glycol. of the formula:

wherein n represents numbers between 2 and 6, R is hydrogen or a methyl group and the compound of the formula (I) or its mixtures possess hydroxyl numbers of about 100 to about 200 (the sum of the percentages of the compounds designated (a) to (f) in each case being 100) are employed as the component (f).

The polypropylene glycol radicals contained in the component (f) have a molecular weight of about 200 to about 500. These hydroxyalkyl esters of methacrylic acid or acrylic acid possess hydroxyl numbers of about '100 to about 200. The particularly preferred hydroxyalkyl esters of acrylic or methacrylic acid have hydroxyl numbers of about 130 to about 150,

Suitable solvents for the copolymers used according to the invention are the customary alkylbenzenes, such as toluene, xylene or mesitylene, or alkylnaphthaleneswith boiling points of about 180 C to 270 C., alcohols, such as nand -i-butanols, monoethers of diols, such as ethanediol monomethyl'ether, and diethylene glycol monobutyl ether, esters of alkanols, such as ethyl acetate, and monoethermonoesters of diols, such as ethanediol monomethyl ethermonoacetate as well as. mixtures of such substances with' one another or'with the addition ofhydrocarbons with boiling points of about 180, C. to .280? -C.

The copolymers can be manufactured in the usual manner, in general appropriately bysolution polymerization in such solvents as are also to-be constituents'of the finished stoving lacquers. .The polymerization can appropriately be initiated by. the customaryinitiators or initiator systems of initiators and activators. I

Suitable polymerization initiators for the manufacture of jthe copolymers used according to the" invention are all compounds which form free radicals under the reaction conditions. Peroxy compounds and azonitriles are preferred. Examples of suitable peroxy compounds are dibenzoyl peroxide, di-terti-butyl peroxide, dioctadecyl 'peroxide, t-butyl peroxypivalate, disuccinoyl'peroxide, urea peroxide, peracetic' acid and perbenzoic acid, alkyl-dialkyl boronperoxides and alkalipersulphates,.perborates and percarbonates, in each case by themselyesor in combination with a reducing agent. Suitable azonitriles are, for example,

1,1 azodicyclohexanecarbonitrile,

u,a'-azobisisobutyronitrile) a,oc'-aZObiS-( a,'y-dimethylvaleronitrile a,a'-a'zobis-(a-methyleneanthronitrile), a,a-azobis- (a-phenylpropionitrile u,oc'-aZ0biS- (a-cyclohexylpropionitrile) a,oL'-3.Z0biS- o-methyl-' -carboxybutyronitrile) disodium ,'y'-azobis-('y-cyanovalerate) and 1-, l -azo dicamphanecarbonitrile.

' Tert.-butylperoctoate being the most preferred polymerization initiator, because no further regulator is required.

The degree of polymerization and hence the viscosity of the copolymers is adjusted to the desired level by the conjoint use of customary regulators, such as mercaptans and aldehydes. As chain-regulating mercaptans, if any, butylmercaptan, octylmercaptan, laurylmercaptan and tert.-dodecylmercaptan are preferentially employed.

A preferred process for the manufacture of the new copolymers used consists of allowing the monomer mixture, including the polymerization catalysts and optionally chain regulators, separately or as a mixture, to run uniformly, over a period of about one to four hours, into the solvent mixture heated to -125 C., the mixture consisting of aromatic solvents of boiling point 180 C. to 270 C. and butyldiglycol or ethyldiglycol, the ratio of aromatics to glycol-ethers being allowed to be between 1:1 and 2:1 parts by weight, under an inert gas, preferably nitrogen; in this process, the polymerization temperatures. should be between 80 C. and about C. The polymerization is then continued for approximately 2 to 8 hours longer in order to achieve as complete a conversion of the monomers as possible. In order reliably to exclude gel formation during the polymerization, the polymerization temperature should not even briefly exceed C. in the case of the abovementioned solvent mixtures, but should instead as far as possible remain within the indicated temperature range.

In the preferred embodiment of the process for the manufacture of the copolymers used the polymerization initiators or catalystsare employed in amounts of 0.8, to 1.5% by weight, relative tothe weight of the monomer mixture, (ii-tertiary butyl peroxide or better tertflbutylperoctoate being most. appropriately employed. In the preferred embodiment of the manufacture of the copolymers, the chain regulators, if any, are employed amounts of 0.1 to 1.5% .-by weight, relative to the weight of the monomer mixture, tertiary dodecylmercaptan being most appropriately employed.

- The improvements in the copolymers, and inthe stoving lacquers which canbe manufactured therewith, which are achieved by a quantitative and also aspecial qualitative selection of the monomeric components (a) to (f) were surprising and unforeseeable, particularly since it had to be expected that as aresiilt of the low proportion ofthe component (a), thermoplastic properties ofthe copolymers would largely have resulted after stoving. It was all the more surprisingthat when using the copolymers manufactured from the components (a) to (f) stoving lacquers. were obtained which after stoving show a suflicient degree of crosslinking which makes it -possible to obtain solvent-resistant and extremely elastic'lacquerll'lgS. r 7 Suitable copolymers areespecially those which are dissolved as a: 50% strength solution in a solvent mixture based on hydrocarbons (aromatic solvents based on 80% byweight of aromatic hydrocarbons and 20% by weight of aliphatic hydrocarbons, of boiling point 208? C. to 254 ,C.) andbutyldiglyeol (weight ratio of hydrocarbonsjto butyldiglycol, 60.40) and have a viscosity of about Z toZ according to Gardner-Holdt. v Y

The copolymers used according to the invention are especially distinguished inthat they have an improved pigment binding capacity and that the lacquerings manufactured with them develop their valuable properties prac tically completely already at relatively short stoving times (for example 1 to 3 minutes) at 260 C. Furthermore,

lacquers manufactured from such copolymers yield lac querings of improved adhesion and impact strength and having particularly pronounced elasticity and hardness.

Lacquerings are obtained which also possess other propafter being bent about 180 around a sheet of equal sheet strength.

By a bend test value of 2 there has to be understood: a lacquered deep drawing sheet shows no lacquer cracks after being bent about 180 around a sheet of twice the sheet strength.

By a bend test value of 3 there has to be understood: a lacquered deep drawing sheet shows no lacquer cracks after being bent about 180 around a sheet of three times the sheet strength.

Films of bend test value have the best elasticity and films of bend test value 3 have a very good elasticity whereas the values 4 and 5 also still represent good elasticity.

From the copolymers used according to the invention it is possible to manufacture stoving lacquers which, if desired, contain the additives which are customary in stoving lacquers, such as pigments, soluble dyestuffs, optical brighteners and agents for promoting levelling and gloss. In particular other customary lacquer binders, such as alkyd resins, aminoplast resins, phenoplast resins, epoxide resins, cellulose derivatives and polymers not identical to the copolymers which are used in this invention can be present, dissolved and/or dispersed in the stoving lacquers in addition to the copolymers. The weight ratio of the copolymers to the additional other lacquer binders should in general preferably be greater than 1 and in particular greater than 2. The addition of the other customarylacquer binders'to the copolymers must be so chosen as to type and amount that clear solutions are obtained and that after the stoving process clear films result. Furthermore, it has generally proved desirable that the weight ratio of the solvents to the total binder constituent in the stoving lacquers should be approximately from 0.4 to 3, in particular approximately from 0.6 to 1.5. t

For manufacturing the lacquerings, the stoving-lacquers based on the new copolymers can be applied to the articles to be lacquered by using the customary methods, for example, by spraying, brushing, pouring, roller-application, flooding, dipping or impregnation. 'The lacquerings can ingeneral be stoved appropriately at temperatures of approximately 180 "to 300 0., especially approximately 240 to 260 C. and for a period of approximately 0.5 to 4 minutes, especially approximately 0.5 to 2 minutes, depending on the temperature. Since the valuable properties of the lacquerings manifest themselves especially on metals such as iron,"aluminum magnesium and alloys of these metals, the stoving lacquers are above all suitable for lacquering articles made of sheet metal, for example parts of coachwork, boats and refrigerators and also cans, jugs, buckets and industrial and domestic appliances. The stoving lacquers can'be used equally well for the production of primer coats and of top coats; because of their adhesion, they are furthermore very suitable for the manufacture of one-coat lacquerings on metals, and the high surface gloss in general makes subsequent polishing superfluous. If the lacquers are to be stoved at lower temperatures, say 180 C. for- 2 to 4 minutes, and/or stoving lacquers are used which contain 8v relatively little copolymerized acrylic or methacrylicacid in the copolymer, it may be advisable to stove the stoving lacquers in the presence of curing agents. Suitable curing agents are the acids or acid-eliminating substances which are customary for curing polymers, for example p-toluenesulphonic acid, maleic acid, phosphoric acid and tartaric acid. The amount of. the curing agent should in in general appropriately be about 0.01 to 5, especially about 0.1 to 2, percent by weight of the copolymers.

The stoving lacquers are preferably used as one-coat lacquers, with the 'said' copolymers as the sole binder. If, however, stoving lacquers or multi-coat stoving lacquers of particularly high solvent resistance and outstanding surface hardness and retention of gloss on exposure to the weather are required, the said copolymers are used in combination with aminoplasts.

Preferred aminoplasts are condensation products of formaldehyde and melamine, wherein about 4 to 6 mols of formaldehyde have been reacted per mol of melamine under either weakly acid or weakly basic conditions, and these products should be etherified ahnost completely, approximately to 100%, with butanol, isobutanol or methanol. The reaction products resulting therefrom should have a molecular weight of about 300 to 1,200 and should be soluble in organic solvents such as xylene and butanol, isobutanol, methanol or glycol-ethers and other alcohols. Formulations for suitable melamine resins are to be found as examples in Swiss Patent Specification 480,3 80 and in German Published Specification 1,127,083.

The copolymer and the aminoplast resin are dissolved in the organic solvent in the ratio of to parts by weight of the copolymer and 5 to 15 parts by weight of the aminoplast resin. The ratios of the amounts of the copolymers and of the alkylated aminoplast should be so chosen that the two components are compatible both in the coating solution and in the finished film. Any suitable concentration of the copolymer and of the aminoplast in the solvent, for example from 1 to 50% by weight, can be used, given the above proviso. If a pigment is present, ,thetotal solids content in the coating composition is between 5 and 75% by weight. The ratio of pigment to hinder (copolymer plus aminoplast) can be between 1:20 and 122.

Set forth below. are several specific examples of the invention. These examples, being illustrative, are not to be construed as limiting. All parts and percentages are by weight unless otherwise specified.

Manufacture of the copolymer solution 1 The following mixture: 52 g. of styrene, 228 g. of ethyl acrylate, 64 g. of methyl methacrylate, 8 g. of acrylic acid, 31 g. of a 65% strength by weight solution of the hydroxy-alkyl ester of methacrylic acid in xylene which is an esterification product of methacrylic acid and poly-. propylene glycol of hydroxyl number about 130, 43 g. of a 65% strength by weight solution in butanol of the ether of methylolmethacrylamide with n-butanol, present as part of a reaction batch produced from 4 mols of methacrylamide, 4.67- mols of paraformaldehyde, 8 molsof n-butanol and 0.03 mol of maleic anhydride with warming and extensive removal of water. 1.8 g. of dodecylmercaptan and 6 g; of p-tert.-butyl peroxide, is added dropwise uniformly over the course of one hour under a nitrogen atmosphere to a mixture consisting of 178 g. of solvent based on about 80% by weight of aromatic hydrocarbons and about 20% by weight of aliphatic hydrocarbons, or boiling point 208 C. to 254 C., and 178 g. of butyl-diglycol, at C., in a flask equipped with a stirrer, reflux condenser and thermometer. Polymerizationis subsequently continued for a further 6 to 8 hours at Crunder a nitrogen atmosphere, until the solution has a solids content of 51% by weight and the viscosity is Z according to Gardner-Holdt.

9 EXAMPLE 1 Use of the copolymer 1 196 g. of this copolymer solution 1, 100 g. of titanium dioxide pigment (rutile) and 70 g. of a mixture consisting of equal parts of butyldiglycol and of solvent based on about 80% by Weight of aromatic hydrocarbons and about 20% by weight of aliphatic hydrocarbons of boiling point of 208 to 254 C. are homogenized for 48 hours on a ball mill. The lacquer was subsequently applied to Erichsen deep-drawing metal sheets with a lacquer spatula, the solvent was allowed to evaporate and the lacquer was stoved at 260 C. for 90 seconds, 120 seconds and 150 seconds. Glossy, white lacquerings with pendulum hardnesses of 84, 113 and 128 and 157 seconds, according to Konig, are obtained; furthermore, these lacquerings show an impact deep-draw (reverse impact test) of 80 inch-pound according to Gardner as well as excellent values in the bend test (1 to 2).

Manufacture of copolymer solution 2 7 1 208 and 254 C., and 150 g. butyldiglycol. The following monomer mixture consisting of 42 g. styrene, 253 g. ethylacrylate, 70 g. methyl-methacrylate, 12 g. acrylic acid, 37 g. of a 65% strength by weight solution in butanol of the ether of methylolmethacrylamide with nbutanol, present as part of a reaction batch manufactured from 4 mols methacrylamide, 4.67 mols of paraformaldehyde, 8 mols of n-butanol and 0.03 mol maleic anhydride with warming and extensive removal of water, and 14 g. of a 70% strength by weight solution of the hydroxylalkylester of methacrylic acid in xylene, which is an esterification product of methacrylic acid and polypropylene glycol, the esterification product having a hydroxyl number about 130, and 3 g. tert.-butylperoctoate is employed.

The dodecylmercaptane used in the copolymer 1 is not hereby employed.

The admission time for the monomer mixture amounts to 2 hours and thereafter the reaction mix is kept at 90 C. for another hours in order to complete the polymerization reaction until the solids content is 51.8% by weight. The obtained solution has a viscosity of Z according to Gardner-Holdt at 20 C. i

manufacture of 10 The coatings being prepared with the aid of copolymer 2 give highly glossy films having a top hardness of about 110 seconds according to Ktinig and a reverse impact test value of 160-inch-pound. according to Gardner.

Because of these properties the copolymer 2 is excel- :lently suited as binder for the manufacture of stoving lacquers determined for the coil coating process.

The stoving lacquers of this invention which are prepared using the above described copolymers can be made to have improved top hardness without showing less good bend test values and reverse impact test values according to Gardner by the addition of micronized polyalkylene wax, for example polyethylene, preferably polypropylene, of an average molecular weight of between 1,000 and 10,000, a specific gravity of 0.8 to 0.9, melting point of about 140 C. and a particle size of below In, preferably of below 0.5/4, in amounts of 0.05 to 2% by weight relative to the solids content of the copolymer. This specific embodiment of the invention is shown by the following examples:

EXAMPLE 3 EXAMPLE 4 A stoving lacquer is produced using the copolymer 2 as being described in Example 2, but additionally 1% by weight of polypropylene wax (polypropylene) having a melting point of 140 C., an average molecular weight of 4,000 to 7,000 and a particle size of 0.5 and 10% by weight of an epoxy resin based on the reaction product of bisphenol A and epichlorohydrin in alkaline medium, having an epoxy equivalent weight of about 400 and a melting point of C.

Stoving lacquers being prepared by Examples 2, 3 and 4 are applied to deep drawing sheets in such a manner that the dried coatings show a filmthickness of 25-30p.. These lacquered test sheets were stoved at 260 C. for 90, 120, 150 or 180 seconds. The film thickness after stoving, the pendulum hardness according to Konig, the visual nail hardness, bend test values, reverse impact strength and the cross-cut with Erichsen deep-drawing value were determined. The results of these test series are presented in the following table:

TECHNICAL TEST VALUES 0F COIL-COATING LACQUERS (Stoving temperature 260 0.)

Reverse Cross-cut Film impact and Erich- Stoving thick- Pendulum Neil strength, sen deep time ness hardness hard- Bend inch drawing, in sec. in sec. ness test pound 8 mm.

Example 2 25-30 77 5 0 0 30 97 5 0 160 0 150 30 100 5 0 160 0 v 180 30 103 5 1 0-1 Example 3.--.:.' z 90 25-30 78 2 0 140 0 120 30 v 103 2 0 160 0 30 108 1 0 140 0 180 25-30 109 1 1 120 0 Example4 90 25-30 7s 2 o 100 120 30 9s 1 0 0 150 so 107 1 o 120 0 so 109 1 1 120 0 0 EXAMPLE 2 COMPARISON TESTS TO SHOW THE ADVANCE OVER THE ART Use of copolymer 2 70 As being described in Example 1 a stoving lacquer is manufactured from the copolymer solution 2 by pigmenting with titanium dioxide in the ratio of 110.6. The applied coatings are stoved at 260 C. for 1 /2 to 3 minutes. The coatings then show a bend test value of 0.

The resin of Copolymer 2 of the present invention was employed to prove the advance over the art.

Test 1 A self-curable acrylate resin called Luprenal LR 8303 of BASF, Ludwigshafen/Rhein, was employed as comparable commercial product being similar but not identical.

Of both comparable resins white lacquer paints were produced according to the instructions given in Example 1 of this invention and the paint was applied to deep drawing sheets as film using a lacquer spatula. After 15 minutes air-drying the lacquerings were stoved at 260 C. for 90, 120, 150 and 180 seconds. The thickness of the stoved coatings amounted to 30a.

The coatings were subjected to the following tests: pendulum hardness according to Konig, nail hardness, bend test, reverse impact strength in inch pound according to Gardner, cross-cut and Erichsen deep drawing value.

The test results are given in the following table:,

TECHNICAL TEST VALUES OF COIL-COATING LAC UERS (stoving temperature 260 C.)

importance for the coil coating process. A pendulum hardness of about a hundred seconds is absolutely necessary to insure good top hardness, one of the conditions for improved corrosion resistance. So the coatings of the present invention combine excellent elasticity with very good hardness neither of which properties can .be obtained by the compared products of Mabrey and of Rohm & Haas because of a low degree of cross linking of their copolymers.

This comparison test shows that the present invention presents lacquers, the stoved films of which have surprisingly excellent reverse impact strength. This property makes it possible to subject the lacquered sheets also to Reverse Cross-cut Film impact and Erich- Stoving thick- Pendulum Nail strength, sen deep time ness hardness hard- Bend inch drawing. in see. (u) in sec. ness test pound 8 mm.

90 25-30 77 5 100 0 i 120 so 97 s 0 160 0 g 150 so, 100 a e 0 160 0 180 30 103 a 1 140 0-1 90 25-30 74 0 2o 0 Luprenal LR 120 30 88 0 0 8303 as 150 9s 5 0 20 0 arison resin. P 180 so 102 a 1 1o 0 Test 2 sudden deformation without damaging the lacqurered sur- A heat hardenable resin composition was prepared according to Example 3, Composition 13, of US. Pat. 3,- 453,345 to Mabrey and coatings were prepared on four deep drawing sheets as described in Test 1, having a film thickness of 26 to 28 1,.

Test 3 face.

It will be obvious to those skilled in the art that other changes and variations can be made in carrying out the present invention without departing from the spirit and scope thereof as defined in the appended claims.

What is claimed is:

1. Stoving lacquers for the coil coating procedure comprising organic solvents and film-forming copolymers of styrene, acrylic acid or methacrylic acid, N-alkoxyal'kylacrylic acid amides or N-alkoxyalkylmethacrylic acid amides, hydroxyalkylacrylates or hydroxyalkyl methacrylates, 'ethylacrylate and methylmethacrylate, the copolymers of which are still soluble in organic solvents and have been produced in a two-step method wherein TABLE Orosscut Reverse p s Stoving Pendulum impact 'Eriehsen time in hardness Pencil strength, eep

sec. at in see. hard- Bend inch drawing, Yellowing 260 C. (Kiinig) ness test pound 8mm. visually Surface Example 2 of the present 77 H 0 0 0 Completely dry.

invention.

97 H '0 160 0 0 Do. 100 H 0 0 0 Do. 103 H 140v 0-1 0 Do.

Test2 90 13 H13 0 120 4 2 Tacky.

120 21 H13 2 120 4 2-3 Slightly tacky. 150 29 HB- 2 120 3-4 4 Do. 180 30 BB 3 120 3-1 4 Do.

Test3 90 I 21d I i u 0 i 0 0 Strongly tacky.

120 10 B 1 140 a 1 Slightly tacky. 150 14 B' 1 140 3-4 2 Do. 180 16 BB 1 120 a 2-3 Do.

The table shows that the coatings prepared according (1') an ether of N-methylolacrylamide or N-methylolto 'Rohm & Haas and Mabrey do not havega completely methylacrylamide is made by warming 1 mol of acrylcured and non-tacky surface. Yellowing of these coatings amide or methacrylamide, 1 to 1.5 mols of paraformhas also been observed. 65 aldehyde, 1 to 3 mols of a saturated alcohol of l to The most surprising testing result manifests itself in 8 carbon atoms and maleic anhydride as the catalyst, a comparison of the obtained pendulum hardness a n d the and combined cross-cut and deep drawing value. Although (2) a mixture of Mabrey uses 73% of the elastic component ethylacrylate (a) 4 to 11% by Weight of this pre-formed ether of and Rohm & Haas even uses 85%, the present invention 70 N-methylolacrylamide or N-methylolmethacrylsurprisingly achieves a much better cross cut and Erichsen amide, deep drawing value with improved bend test results also (b) 10 to 30% by weight of styrene, w1th ust the use of 61% of the elastic component. The 1 to 3% by weight of acrylic acid or methacrylic elastic properties of the obtained coatings in combinaacid, tion with very good pendulum hardness is of tremendous 75 (d) 55 to 65% by weight of ethylacrylate,

wherein n represents numbers between 2 and 6, R is hydrogen or a methyl group and the compound of the formula (I) or its mixtures possess hydroxyl number of about 100 to about 200, and the sum of the percentages of components (a) to (f) is in each case 100, was poured over a period of about one to four hours, into a solvent mixture heated to 80125 C. and consisting of a mixture of aromatic solvents of boiling point 180 to 270 C. and butyldiglycol or ethyldiglycol, the ratio of aromatics to glycol-ethers being between 1:1 and 2:1 parts by weight, under an inert gas, and the polymerization was then continued for approximately 2. to 8 hours in order to achieve as complete a conversion of the monomers as possible.

2. Stoving lacquers according to claim 1, wherein in step (1) nor isobutanol has been employed as the satu rated alcohol with l to 8 carbon atoms.

3. Stoving lacquer according to claim 1, wherein in step (2) the following mixture has been employed:

(a) 6 to 9% by weight of an ether of N-methylolacrylamide or 'N-methylolmethacrylarnide with n-butanol,

(b) 10 to 20% by weight of styrene,

(c) 1 to 3% by weight of acrylic acid or methacrylic acid,

(d) 55 to 65% by weight of ethyl acrylate,

(e) 5 to 20% by weight of methyl methacr'ylate and (f) 4 to 8% by weight of hydroxyalkyl esters of methacrylic acid, of the formula (I) already mentioned.

4. Stoving lacquer according to claim 1 wherein in step (2) the following mixture has been employed:

(a) 5.8% by weight of the ether of N-methylohnethacrylamide with n-butanol,

(b) 10.2% by weight of styrene,

(c) 2.8% by weight of acrylic acid,

(d) 61.9% by weight of ethylacrylate,

(e) 17.1% by weight of methyl methacrylate and (f) 2.2% by weight of hydroxyalkylester of methacrylic acid of the formula (I) wherein n is 4.

5. Stoving lacquer according to claim 1, wherein micronized polyalkylene wax is contained therein additionally to the copolymer.

6. Stoving lacquer according to claim 5, wherein as polyalkylene wax polyethylene or polypropylene of an average molecular weight of 1,000 to 10,000, a density of 0.8 to 0.9, a melting point of about 140 C. and a particle size of below 1,11. is contained.

7. Stoving lacquer according to claim 6, wherein the micronized polyalkylene wax is contained in 0.05 to 2% by weight relative to the solids content of the copolymer.

8. Method for preparing a coating which comprises: (A) applying to the substrate a stoving lacquer composition comprising organic solvents and film-forming copolymers of styrene, acrylic acid or methacrylic acid, N-alkoxyalkylacrylic acid amides or N-alkoxyalkylmethacrylic acid amides, hydroxyalkylacrylate or hydroxyalkyl methacrylates, ethylacrylate and methylmethacrylate, the copolymers of which are still soluble in organic solvents and have been produced in a twostep method wherein (1) an ether of N-methylolacrylamide or N-methylolmethacrylamide is made "by warming 1 mol of acrylamide or methacrylamide, 1 to 1.5 mols of paraformaldehyde, 1 to 3 mols of a saturated alcohol of l to 8 carbon atoms and maleic anhydride as the catalyst, and

( 2) a mixture of (a) 4 to 11% by weight of this pre-formed ether of N-methylolacrylamide or N-methylolmethacrylamide, from step (1),

(b) 10 to 30% by weight of styrene,

(c) 1 to 3% by weight of acrylic acid or methacrylic acid,

(d) 55 to 65% by weight of ethylacrylate,

(e) 5 to 20% by weight of methylmethacrylate and (f) 2 to 10% by weight of hydroxyalkyl esters of methacrylic acid or acrylic acid, of the following formula O-CHa- H wherein n represents numbers between 2 and 6,

R is hydrogen or a methyl group and the compound of the formula (I) or its mixtures possess hydroxyl numbers of about 100 to about 200, and the sum of the percentages of components (a) to (f) is in each case 100,

was poured over a period of about one to four hours, into a solvent mixture heated to 80-125 C. and consisting of a mixture of aromatic solvents of boiling point 180 C.

to 270 C. and butyldiglycol or ethyldiglycol, the ratio of aromatics to glycolethers being between 1:1 and 2:1 parts by weight, under an inert gas, and the polymerization was then continued for approximately 2 to 8 hours in order to achieve as complete a conversion of the monomers as possible, and

(B) baking the coated substrate at a temperature of about 180 to about 300 C. for about 0.5 to 4 minutes. 9. Method of claim 8 wherein the substrate is metal. 10. Method according to claim 8 wherein in step (1) nor isobutanol has been employed as the saturated alcohol with 1 to 8 carbon atoms.

11. Method according to claim 8, wherein in step (2) the following mixture has been employed:

(a) 6 to 9% by weight of a pre-formed ether of N- methylolacrylarnide or N-methylolmethacrylamide with N-butanol,

(b) 10 to 20% by weight of styrene,

(c) ldto 3% by weight of acrylic acid or methacrylic aci (d) 55 to 65% by weight of ethyl acrylate,

(e) 5 to 20% by weight of methyl methacrylate and (f) 4 to 8% by weight of hydroxyalkyl esters of methacrylic acid of the formula (I) 12. Method according to claim 8, wherein in step (2) the following mixture has been employed:

(a) 5.8% by weight of the pre-formed ether of N-methylolmethacrylamide with n-butanol,

(b) 10.2% by weight of styrene,

(c) 2.8% by weight of acrylic acid,

(d) 61.9% by weight of ethylacrylate,

15 (e) 17.1% by weight of methyl methacrylate and (f) 2.2%.by weight of hydroxyalkylester of methacrylic acid of the formula (I) wherein n is 4.

13. Method according to claim 8, wherein micronizcd polyalkylene wax is contained therein additionally to the copolymer.

14. Method according to claim 13, wherein as polyalkylene wax polyethylene or polypropylene of an average molecular weight of 1,000 to 10,000, a density of 0.8 to 0.9, a melting point of about 140 C. and a particle size of below 1 is contained.

15. Method according to claim 14 wherein the micronized polyalkylene wax is contained in 0.05 to 2% by weight relative to the solids content of the copolymer.

1 6 References Cited UNITED STATES PATENTS 3,453,345 7/1969 Mabrey 260'80.75

' FOREIGN PATENTS 1,102,410 3 /1961 Germany.

MORRIS LIEBMAN, Primary Examiner 0 P. R. MICHL, Assistant Examiner US. Cl. X.R.

260-312 N, 33.6 UA, 80.73

UNfiED STATES PATENT OFFICE CERTIFECATE OF CORRECTION Patent No. 3,812,067 Date May 21, 1974 Themistoklis Katsimbas, et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columnl, line '37: "Jan. 25, 1971" should be Jan. 25, 1972---.

Column 1, line 46: "examples" should be -example,-.

Column 1, line 48: "each" should be --such---. I

Column 2, line Q 4: "polyhyldric" should be polyhydric-.

Column 2, line 18: "copolymerable-- should be" -copolymerizable--.

Column 2 line 34: "monomesr" should be -monomers-.

Column 2, line 43: "specication" should be v--specification--.

Column 3, line 26: "="'between H 0 and C should be Column 4, line 40: "methaccrylamide" should be--methacrylamide Column 6', line 72: "60.40" should be --60:40--.

Columnll, line 39: "Rohn" should be --Rohm-'-.

Columnl2, Claim 1: "N-methylolmethylacrylamide" should be -N-methylolmethacrylamide--.

Signed and sealed this 12th day of November 1974.

(SEAL) Attest:

McCOY 1* GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO'WSO uscoMM-oc 60376-P69 U,S. GOVEWNMENY PRINYING OFFICE: l9, 0*"356'13 

